Git-flow and master with multiple parallel release-branches

We are trying to adopt the successful Git branching model implemented by git-flow. Now, we are working on at least two release-branches, one for the latest stable release and one for the next ("preview") release. What I don't understand is why all releases seems to "linearized" to the master and tagged there. Why not tag the releases in their release branches? Why the master at all? Or why a develop branch and not use master for it?

In the git-flow model, your "latest released" version actually maps to the master, while your "preview release" maps to a git-flow release branch. It is forked from develop and finally merged into master when the actual release happens. Then this will become your "latest release" and you will usually fix only bugs for that release, using git-flow hotfixbranches. In this way, your master always represents the most stable state of your latest released version.

If you want to fix bugs for older releases or do any other develop there, you will fork a support branch from the appropriate commit in master (you will have all versions ever created there). support branches are still experimental (according to the docs) and are not well documented. But as you can see from the command line help:

these branches are just started and not intended to be merged back to master nor develop. This is usually fine, as fixes to "ancient" releases or features requested by customers to be implemented in "ancient" releases can't or should not go back into master. If you still think, you want to port a fix to your main development line (represented by master and develop), just start a hotfix, cherry-pick your changes and finish the hotfix.